An expression for the Flory constant ϕ is derived according to which ϕ should depend on the polymer-solvent pair and the temperature. The variations of ϕ, [η], and k, the latter two being fundamental terms in the equation,C/ηSP=1/[η] - kC, are utilized for the determination of the unperturbed dimension of polymer molecules in solution. The importance of k, and the alternative expression which has been derived for k, are discussed.